SNS junctions in nanowires with spin-orbit coupling: role of confinement and helicity on the sub-gap spectrum

We study normal transport and the sub-gap spectrum of superconductor-normal-superconductor (SNS) junctions made of semiconducting nanowires with strong Rashba spin-orbit coupling. We focus, in particular, on the role of confinement effects in long ballistic junctions. In the normal regime, scattering at the two contacts gives rise to two distinct features in conductance, Fabry-Perot resonances and Fano dips. The latter arise in the presence of a strong Zeeman field $B$ that removes a spin sector in the leads (\emph{helical} leads), but not in the central region. Conversely, a helical central region between non-helical leads exhibits helical gaps of half-quantum conductance, with superimposed helical Fabry-Perot oscillations. These normal features translate into distinct subgap states when the leads become superconducting. In particular, Fabry-Perot resonances within the helical gap become parity-protected zero-energy states (parity crossings), well below the critical field $B_c$ at which the superconducting leads become topological. As a function of Zeeman field or Fermi energy, these zero-modes oscillate around zero energy, forming characteristic loops, which evolve continuously into Majorana bound states as $B$ exceeds $B_c$. The relation with the physics of parity crossings of Yu-Shiba-Rusinov bound states is discussed.Comment: 12 pages main article, 14 figures + 5 pages supplementary material, 5 figures. Added new appendix. Other minor changes. Published versio

Multiple Andreev reflection and critical current in topological superconducting nanowire junctions

We study transport in a voltage biased superconductor-normal-superconductor (SNS) junction made of semiconducting nanowires with strong spin-orbit coupling, as it transitions into a topological superconducting phase for increasing Zeeman field. Despite the absence of a fractional steady-state ac Josephson current in the topological phase, the dissipative multiple Andreev reflection (MAR) current I_dc at different junction transparencies is particularly revealing. It exhibits unique features related to topology, such as the gap inversion, the formation of Majorana bound states, and fermion-parity conservation. Moreover, the critical current I_c, which remarkably does not vanish at the critical point where the system becomes gapless, provides direct evidence of the topological transition.Comment: Published version, 21 pages, 7 figures, 3 appendice

Majorana splitting from critical currents in Josephson junctions

A semiconducting nanowire with strong Rashba spin-orbit coupling and coupled to a superconductor can be tuned by an external Zeeman field into a topological phase with Majorana zero modes. Here we theoretically investigate how this exotic topological superconductor phase manifests in Josephson junctions based on such proximitized nanowires. In particular, we focus on critical currents in the short junction limit (LNâ‰ξ, where LN is the junction length and ξ is the superconducting coherence length) and show that they contain important information about nontrivial topology and Majoranas. This includes signatures of the gap inversion at the topological transition and a unique oscillatory pattern that originates from Majorana interference. Interestingly, this pattern can be modified by tuning the transmission across the junction, thus providing complementary evidence of Majoranas and their energy splittings beyond standard tunnel spectroscopy experiments, while offering further tunability by virtue of the Josephson effectWe acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through Grant No. FIS2015-65706-P (MINECO/FEDER) (P.S.-J), No. FIS2015-64654-P (R.A.), No. FIS2016-80434-P (AEI/FEDER, EU) (E.P.) and the Ramón y Cajal programme through Grant No. RYC-2011-09345 (E.P). J.C. and A.B.S. acknowledge financial support from the Swedish Research Council (Vetenskapsrådet), the Göran Gustafsson Foundation, the Swedish Foundation for Strategic Research (SSF), and the Knut and Alice Wallenberg Foundation through the Wallenberg Academy Fellows progra

Zero-energy pinning from interactions in Majorana nanowires

Majorana zero modes at the boundaries of topological superconductors are charge-neutral, an equal superposition of electrons and holes. This ideal situation is, however, hard to achieve in physical implementations, such as proximitized semiconducting nanowires of realistic length. In such systems Majorana overlaps are unavoidable and lead to their hybridization into charged Bogoliubov quasiparticles of finite energy, which, unlike true zero modes, are affected by electronic interactions. We here demonstrate that these interactions, particularly with bound charges in the dielectric surroundings, drastically change the non-interacting paradigm. Remarkably, interactions may completely suppress Majorana hybridization around parity crossings, where the total charge in the nanowire changes. This effect, dubbed zero-energy pinning, stabilizes Majoranas back to zero energy and charge, and leads to electronically incompressible parameter regions wherein Majoranas remain insensitive to local perturbations, despite their overlapWe thank K. Flensberg for illuminating discussions. We acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through the Ramón y Cajal program RYC-2013-14645 and RYC-2011-09345, grant Nos. FIS2012-33521, FIS2013-47328-C2-1-P, FIS2014-55486-P, FIS2015-65706-P, FIS2015-64654-P (MINECO/FEDER), and the “María de Maeztu” Program for Units of Excellence in R&D (MDM-2014-0377

Planificación de la franja urbano rural de Santa Eufemia, Córdoba, Argentina

El objetivo de este artículo es mostrar cómo diseñar y evaluar la visión estratégica territorial de la Franja Urbano Rural (FUR) en la localidad de Santa Eufemia, Córdoba, Argentina. La metodología se basa en un procedimiento multicriterio por fases dirigido al gobierno municipal y los actores que éste involucró. En la fase 1, se identificaron los problemas (oportunidades) y aspiraciones locales mediante entrevistas en profundidad. En la fase 2, se diseñó y valoró un menú de alternativas para dos decisiones estratégicas que emergen de las entrevistas: la regulación hídrica (desagües) y la provisión de alimentos de proximidad. En la fase 3, se relevaron las preferencias de los actores y se evaluaron las alternativas mediante el algoritmo Promethee. Las alternativas elegidas fueron incluidas a la visión de FUR y complementan tres decisiones estructurales (localización de un parque industrial, poblamiento urbano futuro y gestión de residuos). Comparada con las prognosis, dichas alternativas presentan mejor performance, aunque se reconocen algunas limitaciones. Una de ellas reduce 50% los escurrimientos hídricos que potencialmente afectarían a la localidad y otra incrementa la producción de alimentos de proximidad 27%, genera excedentes económicos (12 puestos de trabajo) y minimiza significativamente los riesgos de enfermedades zoonóticas y de contaminación por agroquímicos. Ahora bien, las alternativas requieren más inversiones y un esfuerzo político institucional mayor que la prognosis. Por último, los actores valoraron las alternativas diseñadas junto a las tres dimensiones de la sostenibilidad (criterios de comparación) y acordaron avanzar en una decisión de compromiso sobre la visión de FUR.This article seeks to show how to design and evaluate the territorial strategic vision of the Rural-Urban Fringe (RUF) in Santa Eufemia, Córdoba, Argentina. The methodology is based on a multi-phase multi-criteria procedure for the municipal government and the actors involved. In phase 1, local problems (opportunities) and aspirations were identified through in-depth interviews. In phase 2, a menu of alternatives was designed and assessed for two strategic decisions that emerged within the interviews, namely, rainwater drainage and local food provision. In phase 3, the actors’ preferences were revealed, and the alternatives were evaluated using the Promethee algorithm. The chosen alternatives were included in the RUF vision and complemented three structural decisions (location of an industrial park, future urban settlements, and waste management). Compared with the prognosis, the alternatives chosen, have a better performance, although some limitations are recognized. One of the alternatives reduces the water runoff that could potentially affect the locality by 50%. Another alternative increases local food production by 27%, generating an economic surplus (12 jobs) and significantly minimizing the risks of zoonotic diseases and agrochemical contamination. However, the alternatives require more investment and an increased institutional political effort than in the prognosis. Finally, the actors appreciated the alternatives designed with the three sustainability dimensions (comparison criteria) and agreed to move forward on a compromise decision about the RUF vision

Aplicabilidad clínica de la fibroendoscopia flexible de la deglución en una unidad de cuidados intensivos de un hospital de tercer nivel

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Medicina, Departamento de Cirugía. Fecha de lectura: 22-06-201

Aislamiento y caracterizacion del gen xet de Fragaria chiloensis

57 p.Debido a sus peculiares características como color, sabor y aroma, la frutilla nativa chilena (Fragaria chiloensis) promete ser un importante producto agrícola para nuestro país. Desde el punto de vista de su comercialización y conservación, la firmeza del fruto es una propiedad determinante. Actualmente gran parte de lo que corresponde al proceso de ablandamiento ya ha sido esclarecido, sin embargo, todavía no existe un conocimiento cabal de los genes que intervienen en la perdida de firmeza de la fruta. Se sabe que el ablandamiento de los frutos es un proceso que ocurre a medida que estos maduran y son atribuibles a modificaciones en la composición y estructura de los diversos componentes de la pared celular, tales como celulosa, hemicelulosas y pectinas, las cuales son afectadas por una serie de enzimas que desencadenan un relajamiento de la pared por medio de la solubilización y despolimerización de sus componentes. En el caso específico de la frutilla nativa blanca, estudios previos han mostrado que en los frutos se aprecia un fuerte descenso en la firmeza durante el proceso de maduración, específicamente cuando pasan del estadio verde (II) al blanco (III). Debido a esto, el objetivo principal de este proyecto es determinar la importancia que puede tener el gen que codifica para la enzima Xiloglucano Endotransglicosilasa (XET), como factor importante en la degradación de pared celular y por tanto en la pérdida de la firmeza del fruto de Fragaria chiloensis. Para esto se procedió a extraer RNA desde los distintos estadios de maduración del fruto y comparar su expresión utilizando como metodología la Reacción de Polimerasa en Cadena Semicuantitiva (SQ-PCR)

Majorana bound states from exceptional points in non-topological superconductors

Recent experimental efforts towards the detection of Majorana bound states have focused on creating the conditions for topological superconductivity. Here we demonstrate an alternative route, which achieves fully localised zero-energy Majorana bound states when a topologically trivial superconductor is strongly coupled to a helical normal region. Such a junction can be experimentally realised by e.g. proximitizing a finite section of a nanowire with spin-orbit coupling, and combining electrostatic depletion and a Zeeman field to drive the non-proximitized (normal) portion into a helical phase. Majorana zero modes emerge in such an open system without fine-tuning as a result of charge-conjugation symmetry, and can be ultimately linked to the existence of `exceptional points' (EPs) in parameter space, where two quasibound Andreev levels bifurcate into two quasibound Majorana zero modes. After the EP, one of the latter becomes non-decaying as the junction approaches perfect Andreev reflection, thus resulting in a Majorana dark state (MDS) localised at the NS junction. We show that MDSs exhibit the full range of properties associated to conventional closed-system Majorana bound states (zero-energy, self-conjugation, $4\pi$-Josephson effect and non-Abelian braiding statistics), while not requiring topological superconductivity.Comment: 15 pages, 7 figures. Added discussion of non-Abelian braiding properties. Published versio

Reportaje informativo “Noctívagos”.

Exponer las causas por las cuales, algunos trabajadores informales de Villavicencio, inician su jornada laboral en las horas de la noche.Cada noche en Villavicencio - Meta, alrededor de 33.000 trabajadores informales (DANE, 2016), salen a las calles más concurridas de la ciudad a ofrecer sus productos o servicios. Esta labor, que varía según la persona, es la que les brinda una oportunidad para llevar su sustento a casa.Por medio de este reportaje, se logra evidenciar el motivo por el cual, estas personas eligieron la jornada nocturna para empezar con su trabajo; además de esto, hace visible algunas de las experiencias por las que han tenido que pasar y que resaltan la brecha existente entre los trabajadores diurnos y nocturnos